Non-cryogenic production of nitrogen for on-site injection in well clean out

ABSTRACT

There is disclosed a method for cleaning out of a well in which a compressed inert gas, produced by the non-cryogenic separation of air is delivered to the region of the well where particulate matter has collected that inhibits the ability of the well to produce.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of co-pending U.S. patentapplication Ser. No. 09/642,447, filed Aug. 18, 2000, which is hereinincorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention is directed to methods of cleaning outwells using an inert gas. More specifically, the invention is directedto methods of cleaning out wells which employ an inert gas in a regionof the well where collected matter has inhibited the ability of the wellto produce. The inert gas, typically nitrogen gas, is supplied on-siteby the separation of air using a membrane or a pressure swing adsorptionsystem.

[0004] 2. Background of the Related Art

[0005] In the cleaning out of oil or gas or geothermal wells, a fluid istypically delivered to a particular area of the well. For example, in acleaning out operation, fluid must be introduced in the area of the wellto be cleaned to remove the sand, scale or other substances that haveeffected the ability of the well to produce. One such fluid includes afoam consisting of nitrogen gas and liquid. Nitrogen can also becombined with a surfactant, foaming agent or water for differentapplications, like well treating.

[0006] One method of cleaning out a well includes the use of air cooledto cryogenic temperatures. The frozen air not only reduces the threat ofdownhole combustion but also freezes the ground to prevent the influx ofwater during clean out. As is well known, cooling to cryogenictemperatures is costly and requires additional heavy equipment which maynot be readily available, particularly when the well is in a remotelocation like offshore. It is also common to use liquid nitrogen as thesource of gas. Liquid nitrogen, however, is disadvantageous because itis considerably more expensive to use than air and difficult to obtainin remote locations.

[0007] It would therefore be desirable to devise a method by which aninert gas, typically nitrogen gas, may be conveniently and efficientlysupplied to an area of a well to be cleaned out which eliminates theproblems associated with cryogenic nitrogen and other sources ofnitrogen gas.

SUMMARY OF THE INVENTION

[0008] The present invention is generally directed to a method forcleaning out oil and/or gas or a geothermal wells in which a compressedinert gas is delivered to the area of the well where production isinhibited. The inert gas is obtained from an on-site, non-cryogenicsource. In particular, the source of the inert gas is air which ispreferentially separated into an inert gas rich fraction and an oxygenwaste gas fraction such as by membrane separation or by pressure swingadsorption, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] So that the manner in which the above recited features,advantages and objects of the present invention are attained and can beunderstood in detail, a more particular description of the invention,briefly summarized above, may be had by reference to the embodimentsthereof which are illustrated in the appended drawings.

[0010] It is to be noted, however, that the appended drawings illustrateonly typical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

[0011]FIG. 1 is a schematic view of an embodiment of the inventionshowing an above surface apparatus for generating a nitrogen rich gasfrom an air-separation membrane to be delivered to an area of a wellwhere production is inhibited;

[0012]FIG. 2 is a schematic view similar to FIG. 1 in which a nitrogenrich gas is generated by a pressure swing adsorption unit;

[0013]FIG. 3 is a schematic view of a two bed pressure swing adsorptionsystem for generating a nitrogen rich gas;

[0014]FIG. 4 is a schematic view of a surface equipment installationincluding coiled tubing for delivering the inert gas to the area of thewell to be cleaned out;

[0015]FIG. 5 is a schematic view of a wellbore showing an area of thewell inhibited by the accumulation of sand in production tubing; and

[0016]FIG. 6 is a schematic view of the well of FIG. 5 shown during wellclean out using coiled tubing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] The present invention is directed to the on-site, non-cryogenicproduction of an inert gas, typically a nitrogen rich gas and itsdelivery in the cleaning out, treating or servicing of oil and/or gas orgeothermal wells. As used herein “treating” refers to the stimulation orpriming of a well to stimulate a formation in order to increaseproduction therefrom. “Servicing” refers to any number of operationsincluding the pressure testing of downhole tools, like plugs or packersthat seal a wellbore or an annular area within a wellbore. As usedherein the term “nitrogen rich gas” shall refer to a gas containingpredominantly nitrogen gas and no more than 10% oxygen gas by volume.The nitrogen rich gas is produced from air by a number of differentmethods including membrane separation, pressure swing adsorption, vacuumswing adsorption and fuel cells. The methods of production are describedin U.S. Pat. No. 5,388,650 to Michael and that patent is incorporated byreference herein in its entirety.

[0018] Referring to FIG. 1 there is shown an above ground installationfor producing a nitrogen rich gas using membrane separation and fordelivery of the nitrogen rich gas to the drilling region. A feed aircompressor 2 includes an intake port 4 for receiving ambient air and acompressor 6 for pressurizing the air to a suitable pressure, typicallyin the range from about 100 to 350 psig. The compressed air is sentthrough a conduit 8 to an air separation membrane system shown generallyby numeral 10. The membrane is composed of bundles of hollow fiber,semi-permeable membranes which are assembled parallel to a central coretube. The bundle is placed into an outer case to form an air separationmodule. The air is divided into two streams; a nitrogen rich stream anda stream rich in oxygen and water vapor.

[0019] When the compressed air is introduced to the feed side of themembrane fibers, the air travels down the bore of the hollow permeablefibers. Oxygen, water vapor and other “fast gases” pass through to theoutside of the fibers. The oxygen-rich gas stream then flows through thefiber bundle to the periphery of the outer case of the separator systemwhere it is discharged as a by-product. While all but a small fractionof the oxygen passes through the membrane material to the exterior ofthe hollow fibers, most of the nitrogen present in the feed air iscontained within the hollow fiber membrane. As a result, the nitrogenrich gas is effectively separated from the feed air and exits themembrane system 10 via a conduit 12 for entry into an optional boostercompressor 14.

[0020] The booster compressor 14 is employed to elevate the pressure ofthe nitrogen rich gas. The pressure of the gas obtained from the airseparation membrane system 10 is from about 100 to 200 psig. The boostercompressor 14 is capable of raising the pressure of the nitrogen richgas up to or exceeding 4500 psig and even as high as about 10,000 psig,but typically in the range of from about 1,000 to 2,000 psig. The highlycompressed nitrogen rich gas leaves the booster compressor 14 via aconduit 16 and is sent to a surface equipment installation 18 of thedrilling operation as explained in detail hereinafter.

[0021] The nitrogen rich gas may also be produced by a pressure swingadsorption system in accordance with the present invention. Referring toFIGS. 2 and 3, there is disclosed a pressure swing adsorption unit 20having two beds “A” and “B”. It should be understood, however, that thepresent invention is applicable to pressure swing adsorption unitshaving an alternate construction such as a greater number of beds.Referring to FIG. 3, air from a source (not shown) is fed to acompressor 6 to raise the pressure of the air, to accumulate compressedair during the non-production phase and to output compressed air duringpeak loading of the beds. The compressed air is fed to a storage vessel22. The compressed air is then fed via the conduit 24, 26 to an outlet28 leading to bed A and an outlet 30, leading to bed B. Each outlet 28,30 is controlled by respective valves 32, 34. When valve 32 is opened,allowing the compressed air to reach bed A, valve 34 remains closed sothat bed B may undergo regeneration during the depressurization phase ofthe pressure swing adsorption unit 20.

[0022] The compressed air enters the bed A through the open valve 32 viaa conduit 36. The bed A contains at least one adsorption materialcapable of preferentially adsorbing oxygen and other waste gases. Thepreferred adsorbents are selected from molecular sieves and silica gel.As a result, substantially pure nitrogen passes out of the bed A througha conduit 38, a valve 40 and into a nitrogen storage vessel 42 via aproduct line 44 for passage via a conduit 82 to an optional boostercompressor 14, like the one shown in FIG. 1.

[0023] While bed A is producing nitrogen gas, bed B is at atmosphericpressure. Upon completion of the nitrogen production cycle in bed A, thesystem undergoes equalization to raise the pressure in bed B to anintermediate pressure. This is accomplished by closing the nitrogenproduct valves 40, 46 and the compressed air intake valves 32, 34. Thus,the input of compressed air and the output of nitrogen product aretemporarily suspended. Equalization is accomplished by passing a portionof the pressurized gas from the top of the bed A via a conduit 38, valve50, a conduit 52, restrictive orifice 54, through a conduit 56 and intothe top of the bed B. In addition, pressurized gas is passed from thebottom of the bed A via the conduit 36, a valve 58, a conduit 60, arestrictive orifice 62 and a conduit 64 into the bottom of bed B.

[0024] Once equalization is completed so that bed A and B are at similarpressures, bed A undergoes regeneration by depressurizing to atmosphericpressure to remove the oxygen enriched waste gases. This is accomplishedby closing the equalization valves 50, 58 and opening a regenerationvalve 66 for the bed A. The waste gas is then vented to the atmospherethrough a conduit 68 and a restrictive orifice 70. As a consequence, thebed A is regenerated. Further cleansing of the bed A may be made bypassing a purge gas, such as substantially pure nitrogen gas, from asource 72, through conduits 74 and 76, respectively, a valve 78 and intobed A via the line 38. When the bed B is further cleansed, the purge gaspasses through the conduits 74 and 76, respectively, a valve 80 and theconduit 56. After purging, the adsorbents are ready for adsorbing wastegases in a new nitrogen production cycle.

[0025] Since the pressure in bed B has been raised to an intermediatepressure, it is ready to receive compressed air. The compressed air isprovided through the valve 34 and the conduit 64. It may be necessary,in order to get sufficient compressed air to quickly load bed B up tooperating pressure, for the compressed air feed generated by thecompressor 6 to be supplemented by compressed air already stored in thestorage vessel 22. Once bed B has been loaded, the valve 46 is opened,allowing product gas to enter the product line 44 via the conduit 56from which it enters the storage vessel 42. A distribution conduit 82extends from the storage vessel 42 to provide a flow of nitrogen richproduct gas to the booster compressor 14 shown in FIG. 1. After nitrogenproduction in bed B is completed, the valve 46 is closed as is the valve34 to stop the compressed air feed. The equalization circuit isactivated by opening valves 50, 58 and the pressurized gas is fed fromthe top and bottom of bed B to bed A to raise the pressure therein to anintermediate pressure level. Bed B is then depressurized by eliminatingthe oxygen rich waste gases which are sent via the conduits 64, 84through a valve 86 to the atmosphere via the conduit 68 and restrictiveorifice 70.

[0026] Thereafter, compressed air from the compressor 6 and the storagevessel 22 is fed to bed A through the valve 32 via the conduit 36 toraise bed A to the desired operating pressure thereby commencing thenitrogen production cycle from bed A which passes into the boostercompressor 14. The nitrogen rich gas, after compression up to as high as10,000 psig in the booster compressor, 14, is sent to surface equipmentinstallation shown in FIG. 4, where it is used in the cleaning out ofthe well shown in FIG. 5.

[0027] Referring to FIG. 4, in one embodiment, the high pressurenitrogen rich gas is delivered to the wellbore from a source 120 throughcoiled tubing 100. The coiled tubing is charged with the gas at a reel105 and extends through a stripper assembly 110. The flow rate of thenitrogen rich gas is typically measured by an orifice meter and is sentthrough an adjustable choke and a pressure shut off valve (not shown)before entering the wellbore. Foam can be added to the gas if it isrequired for downhole circulation. The foam is used to assist in wellstimulation or removal of the sand, scale or other matter inhibiting theproduction of the well. The surface installation may optionally includean injector manifold for injecting chemicals, such as surfactants andspecial foaming agents, into the nitrogen rich gas feed stream to helpdissolve and carry away particulate matter or to provide a low density,low velocity circulation medium of stiff and stable foam chemicals tocause minimum disturbance to unstable or unconsolidated formations.

[0028]FIG. 5 is a section view of a cased wellbore 200 with productiontubing 202 extending to a location adjacent casing perforations 205. Anannular area 216 is isolated by upper and lower packing members 207,208. The production fluid enters production tubing 202 through aperforated screen member 215. In the preferred embodiment, annular area216 is packed with gravel to encourage migration of production fluidfrom the surrounding formation into the wellbore. As illustrated, sand(shown as 220) has migrated through the perforated screen member 215into the interior of production tubing 202 and inhibited production ofthe well.

[0029]FIG. 6 illustrates one embodiment of the cleaning out method ofthe present invention in progress. Coiled tubing 100 (see also FIG. 4)has been inserted into the production tubing 202 to provide a pathwayfor the flow of pressurized nitrogen rich gas (shown as bubbles 230)from the surface of the well to the area of the well to be cleaned out.As the lower end of the coiled tubing 100 breaches the area of sand inthe production tubing 202, gas is injected into the well via the coiledtubing. An annular area 231 formed between the coiled tubing 100 and theproduction tubing 202 provides a pathway for the return nitrogen richgas and with it, particulate matter, like sand, to the surface of thewell where it is collected and disposed of. The coiled tubing 100 istypically pumped up and down in the area of particulate matter, in orderto agitate the material and to facilitate its removal during the cleanout.

[0030] In operation, the nitrogen rich gas produced by the airseparation membrane system 10 or the pressure swing adsorption unit 20or other non-cryogenic system typically has a nitrogen content of atleast about 85% by volume, preferably at least about 95% by volume, andan oxygen content of no more than 10% by volume, preferably less thanabout 5% by volume. The nitrogen rich gas is sent to a boostercompressor 14 where the pressure is raised to as high as 10,000 psig ormore, typically in the range of about 1,000 to 2,000 psig. Thepressurized nitrogen rich gas is sent to the surface equipment shown inFIG. 4 where it is monitored and metered into the wellbore through thepathway within the coiled tubing 100.

[0031] Because the nitrogen rich gas is under pressure, it swirls aroundthe area to be cleaned out with sufficient force and velocity to carrythe particulates upward into the pathway created within annular area231. The particulate-containing stream then exits the production tubingat the surface of the well where it is carried to a blooey line andeventually discarded into a collection facility, typically at a locationremote from the actual well site.

EXAMPLE

[0032] A typical well cleanout is performed in a series of sequentialsteps. First, nitrogen is produced on site using any of the foregoingmethods. Second, coiled tubing is placed in the well and lowered apredetermined distance to the area of the well where production isinhibited. Third, the gas, as well as foam is introduced simultaneouslyinto the coiled tubing. Fourth, the coiled tubing is pumped up and downin the well to agitate the substance inhibiting production and encourageits removal. Fifth, the return of material at the surface is measuredand monitored. Finally, when the material carried by the return gas hasdiminished to an acceptable level, the cleanout operation isdiscontinued. The flow rate of nitrogen rich gas to the drilling regionof an oil and/or gas well or a geothermal well can vary over a widerange depending on the size of the downhole, the depth of the well, therate of production and, the size of the production tubing.

[0033] A typical cleaning out operation will require the production offrom 1,500 to 3,000 standard cubic feet per minute (scfm) of nitrogengas from an air separation system which can be anyone of a number ofconventional systems including an air membrane separation system or apressure swing adsorption system. The purity of the nitrogen gas mayvary, but is nominally set at no more than about 5% by volume of oxygen.The resulting nitrogen rich gas is then pressurized up to a pressure offrom about 1,500 to 2,000 psig before being passed to the area of thewell to be cleaned out.

[0034] A cleaning out operation will take about two days, although veryclogged wells may require more time. The nitrogen rich gas deliverysystem is designed for continuous operation and all of the nitrogen richgas is generated on-site without the need for external nitrogenreplenishment required for cryogenically produced liquid nitrogendelivery systems.

[0035] While the foregoing is directed to the preferred embodiment ofthe present invention, other and further embodiments of the inventionmay be devised without departing from the basic scope thereof, and thescope thereof is determined by the claims that follow. For example, inaddition to well clean out, the on site production of non-cryogenicnitrogen provides a source of gas for servicing or stimulating a well orfor pressure testing downhole devices like packers, and the invention isnot limited only to the method of cleaning out a well.

1. A well servicing system comprising: a membrane separator forseparating at least a substantial portion of oxygen contained within afluid feed stream to produce a substantially inert gas and a fluidbyproduct; a compressor to increase the pressure of the substantiallyinert gas and to supply the substantially inert gas to a wellbore; and acollector to collect constituents comprising a fluid returning from thewellbore.
 2. The well servicing system of claim 1, wherein the wellservicing system is operated proximate the wellbore.
 3. The wellservicing system of claim 1, wherein the collector separates thesubstantially inert gas from the fluid returning from the wellbore. 4.The well servicing system of claim 3, wherein the separatedsubstantially inert gas is introduced in to the compressor.
 5. The wellservicing system of claim 4, wherein the well servicing system isoperated proximate the wellbore.
 6. The well servicing system in claim1, wherein the substantially inert gas is a nitrogen rich gas.
 7. Thewell servicing system in claim 6, wherein the nitrogen rich gas containsat least 95 percent nitrogen.
 8. The well servicing system in claim 1,wherein the pressure of the substantially inert gas is boosted to atleast 1000 psig.
 9. The well servicing system in claim 1, furtherincluding a coil tubing assembly to supply the substantially inert gasto the wellbore.
 10. The well servicing system in claim 1, wherein thecollector is a three-phase separator.
 11. The well servicing system inclaim 1, wherein an additive is combined with the inert rich gas. 12.The well servicing system in claim 11, wherein the additive is an acid.13. The well servicing system in claim 11, wherein the additive isproppants.